The invention relates to a randomly branched polyamide comprising at least units derived from:
1. AB monomers,
2. at least one compound I, being a carboxylic acid (Av) having a functionality vxe2x89xa72 or an amine (Bw) having a functionality wxe2x89xa72,
3. at least one compound II, being a carboxylic acid (Av) having a functionality vxe2x89xa73 or an amine (Bw) having a functionality wxe2x89xa73, compound II being a carboxylic acid if compound I is an amine or compound II being an amine if compound I is a carboxylic acid.
In the context of this application, with the term xe2x80x9crandomly branchedxe2x80x9d is meant that the branching points are randomly distributed in the polyamide chain.
Such a randomly branched polyamide is known from EP-345.648-B1. However, a problem encountered with the randomly branched polyamide according to EP-345.648-B1 is that the randomly branched polyamide is not intrinsically gel-free so that, while the randomly branched polyamide can for instance be obtained as a gel-free melt, during further processing of the randomly branched polyamide, gel formation may as yet occur. In the context of this application gel formation is understood to be a process involving the formation of a network in a polymer material. Gel formation gives rise to, among other things, the formation of visible inhomogeneities (xe2x80x9cgelsxe2x80x9d) during processing of the randomly branched polyamide into, for instance, films or fibres and to deterioration of the mechanical properties of polyamide objects obtained from the randomly branched polyamide. It is also known that when randomly branched polyamide is processed in equipment where local overheating may take place or where polyamide material may accumulate, for instance in extruders and mixers, it may contain strongly crosslinked polyamide.
It is desirable to have intrinsically gel-free randomly branched polyamide available. In the context of this application xe2x80x9cintrinsically gel-freexe2x80x9d is understood to mean that the composition of the randomly branched polyamide is such that it cannot form crosslinked polyamide (and therefore no gels), in particular during the prepolymerization, the polymerization, the post-condensation, the processing, for instance into films or fibres, and the storage of the randomly branched polyamide, and this at a variety of ambient factors, for instance at elevated temperature and pressure.
Although the prevention of gel formation in polymeric materials has been receiving a great deal of attention in practice, at this point of time neither a structural nor a systematic approach is known to provide an adequate solution to the problem of obtaining intrinsically gel-free, randomly branched polyamide from AB monomers.
It is the aim of the inventors to provide such an intrinsically gel-free, randomly branched polyamide comprising at least units derived from:
1. AB monomers,
2. at least one compound I, being a carboxylic acid (Av) having a functionality vxe2x89xa72 or an amine (Bw) having a functionality wxe2x89xa72,
3. at least one compound II, being a carboxylic acid (Av) having a functionality vxe2x89xa73 or an amine (Bw) having a functionality wxe2x89xa73, compound II being a carboxylic acid if compound I is an amine or compound II being an amine if compound I is a carboxylic acid.
This aim is achieved when the amounts of all units derived from carboxylic acids and amines in the polyamide satisfy formula 1
P greater than 1/[(FAxe2x88x921).(Faxe2x88x921)]xe2x80x83xe2x80x83(1) 
where:
P=[xcexa3(ni.fi)]x/[xcexa3(ni.fi)]yxe2x80x83xe2x80x83(2) 
where Pxe2x89xa71 and either X=A and Y=B, or X=B and Y=A, and
Fx=xcexa3(ni.fi2)/xcexa3(ni.fi)xe2x80x83xe2x80x83(3) 
for, respectively, all carboxylic acids (X=A) and all amines (X=B), where fi is the functionality of either the carboxylic acid (fi=vi) or amine (fi=wi), ni being the number of moles of the carboxylic acid or amine and the summation involving all units derived from carboxylic acids and amines in the polyamide.
In the context of the present invention AB monomer is understood to be a monomer that has both a carboxylic acid group (A) and an amino group (B).
In the context of the present application compound I and compound II are also understood to be mixtures of several carboxylic acids having the same functionality or mixtures of several amines having the same functionality.
In the context of the present application carboxylic acid and amine are understood to be, respectively, a compound which, besides one or more carboxylic acid groups, does not carry any amine groups and the other way round. It therefore follows that units derived from carboxylic acids or amines in the polymer have a chemical composition that differs from chat of the units derived from the AB monomers. Carboxylic acid group is in the context of the present application understood to be a group that can form a covalent bond with an amine group, for instance xe2x80x94COOH, xe2x80x94COHal (Hal=halogen), xe2x80x94CO2R in which R is an alkyl residue with 1 to 20 carbon atoms and xe2x80x94SO2Hal (Hal=halogen).
In the context of the present application functionality is understood to be the number of functional groups in the carboxylic acid or the amine that can form a bond with other carboxylic acids, amines or AB monomers to form the randomly branched polyamide according to the invention A functional group that cannot form this bond, for instance a sterically hindered amine group or an aromatic amine group, is not considered as a functional group in determining the functionality. Likewise, the functionality is equated to 1 if two functional groups at a compound are both involved in a single bond with a third functional group, for instance two COOH groups that are close together which form an imide bond with an amine, for instance in the compound orthodicarboxy-benzene.
Preferably, the functionality v or w of compound I can be chosen from 2, 3, 4, 5 and 6. More preferably, the functionality of compound I is 2. Preferably, the functionality v or w of compound II can be chosen from 3, 4, 5 and 6, more preferably, the functionality of compound II is 3.
Eligible AB monomers are all AB monomers that can be used for the production of polyamides, in particular xcex1,xcfx89-amino acids and/or lactams, for instance caprolactam, laurine lactam and dodecalactam, as well as the corresponding amino acids and aromatic amino acids, for instance p-(aminomethyl)-benzoic acid. Preferably, the lactam is xcex5-caprolactam.
Eligible carboxylic acids (Av) are preferably difunctional carboxylic acids, for instance adipic acid, dodecane dicarboxylic acid, isophthalic acid and terephthalic acid and trifunctional carboxylic acids, for instance 1,3,5-tris(caproic acid)melamine, trimesic acid and trimeric fatty acids with 50-60 carbon atoms as well as esters and anhydrides of said carboxylic acids. Preferably, the difunctional carboxylic acid is terephthalic acid. Preferably, the trifunctional carboxylic acid is 1,3,5-tris(caproic acid)melamine (TCAM) or trimesic acid.
Eligible amines (Bw) are preferably difunctional amines, for instance diaminobutane, diaminohexane, diaminododecane, cyclic amines, for instance 1,4-diaminocyclohexane, 4,4xe2x80x2-diaminobicyclohexylamine, 1,3- and 1,4-xylylene diamine and trifunctional amines, for instance trisaminononane and bis (hexamethylene triamine). Preferably, the difunctional amine is 1,6-hexamethylene diamine. Preferably, the trifunctional amine is bis (hexamethylene triamine).
Besides the units derived from compounds I and II according to the invention also other units derived from carboxylic acids and amines may be present, for instance monofunctional carboxylic acids and amines (chain terminators).
Although the aim of the invention according to ZP-345.648-B1 is not the aim of the present invention, while said publication does not mention the measures according to the present invention, either, it does mention, besides a number of randomly branched polyamides that do not satisfy the measures according to the present invention, also a number of randomly branched polyamides which coincidentally satisfy the measures according to the invention. These randomly branched polyamides are excluded from the application, more specifically the randomly branched polyamides that are built up of units derived from carboxylic acids (Av) having a functionality v and amines (Bw) having a functionality w, in the following amounts (in xcexcmol/g of polyamide):
B1 (20), B3 (60) and A2 (20)
B1 (10), B3 (60) and A2 (30)
B1 (120), B2 (30) and A3 (60)
B1 (120), B2 (30) and A3 (70)
B1 (170), B3 (30), A2 (60) and A3 (60)
The intrinsically gel-free, randomly branched polyamide according to the invention can be produced using methods known to one skilled in the art, both via a batch process and via a continuous process According to a first embodiment all AB monomers, carboxylic acids and amines are polymerized in amounts according to the invention in a reactor at a suitable temperature and pressure According to a second embodiment the carboxylic acids and amines are added to a melt of a polyamide comprising units derived from AB monomers.
The gel-free, randomly branched polyamide according to the invention can also contain the customary additives, for instance flame retardants, fillers, release agents, lubricants and colourants.
The intrinsically gel-free, randomly branched polyamide according to the invention is eminently suitable for the production of fibre, film, foams and moulded articles. In particular, the intrinsically gel-free, randomly branched polyamide according to the invention is eminently suitable for the production of thin film, in particular flat film. The inventors have established that no gels could be observed in said thin film obtained with the polyamide according to the invention. Another surprising advantage of the polyamide according to the invention is that no or hardly any neck-in occurs in the production of flat film. Neck-in is the decrease in the ratio of film width to die width during the film forming process. This surprising advantage allows films to be formed in a simple manner without the known attendant measures to prevent neck-in, for instance cooling of the film edges during the film forming process.
The invention therefore also relates to a process for the production of film obtained from the polyamide according to the invention, as well as to the film obtained with the polyamide according to the invention.
The invention will now be elucidated on the basis of examples, without however being limited thereto.